Engine systems may utilize recirculation of exhaust gas from an engine exhaust system to an engine intake system, a process referred to as exhaust gas recirculation (EGR), to reduce regulated emissions. For example, a turbocharged engine system may include a high-pressure (HP) EGR system which recirculates exhaust gas from the exhaust manifold upstream of the turbocharger turbine to the intake passage downstream of a turbocharger compressor and upstream of the intake manifold. Accordingly, exhaust gas may be recirculated and combined with the fresh intake air from the turbocharger compressor, resulting in a compressed mixture of fresh intake air and recirculated exhaust gas downstream of the compressor. An EGR valve may be controlled to adjust the amount of recirculated exhaust gas flow and achieve a desired intake air dilution, the desired intake air dilution based on engine operating conditions. The HP exhaust gas routed through the EGR system is measured and adjusted based on engine speed and load during engine operation to maintain desirable combustion stability of the engine while providing emissions and fuel economy benefits.
Many engine systems utilize two banks of cylinders arranged in a V formation, also known as a V-engine. Furthermore, in turbocharged V-engines, two turbochargers may be utilized to compress the intake charge. A common configuration is a parallel twin-turbocharger engine, wherein one turbocharger is assigned to one cylinder bank. Furthermore, the two turbochargers operate individually so the compressed charge of one turbocharger is not fed into the inlet of the second turbocharger. In this type of system, each turbocharger is driven by the exhaust from the exhaust manifolds of their respective cylinder banks. If a HP EGR system is also utilized with a parallel twin-turbocharged engine, then a portion of the exhaust from both cylinder banks are routed through an EGR system. An issue that arises with implementation of a HP EGR system with parallel twin-turbochargers is that systems may experience turbocharger boost imbalance which is a result of unequal exhaust gas conduits. Turbocharger boost imbalance may lead to adverse engine operation.
In one EGR system arrangement, shown by Gladden and Mineart in U.S. Pat. No. 8,297,054, an EGR circuit is connected to two cylinder banks arranged in a v-configuration. The engine system includes two main turbochargers that discharge exhaust in parallel to aftertreatment devices in one embodiment. The EGR circuit contains two inlet ports that are fluidly connected to the two exhaust manifolds corresponding to the first and second cylinder banks. Also, the two inlet ports are fluidly connected to an EGR cooler via a fluid passage. High-pressure exhaust at elevated temperatures from the two exhaust manifolds is routed through the inlets into the fluid passage which sends the exhaust through the EGR cooler. The EGR cooler is shown to have a single inlet passage and a single outlet passage through which the exhaust flows.
However, the inventors herein have identified potential issues with the approach of U.S. Pat. No. 8,297,054. With the progression of more compact vehicles that strive to minimize total weight while maintaining engine power and performance, efficient packaging of the engine has become increasingly important. In many EGR systems, the extra ductwork and components required to maintain equal length tubes to avoid turbo imbalance are expensive to add and difficult to package in the limited engine space.
Thus in one example, the above issues may be addressed by an exhaust gas recirculation (EGR) cooler, comprising: a coolant passage with a coolant inlet positioned on a first longitudinal surface of the cooler, fluidically coupled to an external coolant circuit, and a coolant outlet positioned on a second lateral surface of the cooler, fluidically coupled to an external coolant circuit, the second lateral surface opposite and parallel to the first longitudinal surface; a first exhaust passage with an inlet and an outlet located on opposite lateral surfaces, the lateral surfaces perpendicular to the first and second longitudinal surfaces; and a second exhaust passage equal in length to the first exhaust passage, the second exhaust passage including an inlet and an outlet located on the opposite lateral surfaces, the second exhaust passage inlet on the same surface as the outlet of the first exhaust passage, and the second exhaust passage outlet on the same surface as the inlet of the first exhaust passage. In this way, the dual conduit EGR cooler design enables shorter, equal length EGR gas supply tubes and shortens the overall package space required without causing turbocharger boost imbalance or adversely affecting engine performance
For example, each of the exhaust manifolds may be configured with exhaust tubes that direct exhaust gases towards their respective turbines. Upstream of the turbine inlets and downstream of the exhaust manifolds, two supply tubes (one for each cylinder bank) may branch away from the turbines and connect to opposite sides of an EGR cooler. The two supply tubes may enter the EGR cooler and may be routed through the EGR cooler in equal lengths, emerging on opposite sides as discharge tubes. The discharge tubes may then meet to form a combined exhaust conduit that leads away from the EGR cooler to a control valve that adjusts the EGR gas flow into the intake passage and intake manifold of the engine. By using the dual inlet/outlet EGR cooler, EGR gas from both cylinder banks may be equally cooled and merged with the intake charge without adding extra piping.
Furthermore, the EGR cooler may be mounted on a portion of the engine such that the supply tubes for both cylinder banks are symmetrically routed into the EGR cooler. The EGR cooler may be attached perpendicularly to the axis of the crankshaft, reducing the supply piping distance that connects the exhaust passages to the EGR cooler. Additionally, the merged exhaust conduit leading from the EGR cooler to the intake passage may also be reduced in length.
In another example, in order to reduce package space, an engine method is provided, comprising: directing first and second exhaust gases through two separate exhaust passages into first and second opposite sides of an EGR cooler, respectively; directing the still separate first and second exhaust gases out of the EGR cooler through the second and first sides, respectively; and merging the exhaust gases to form a single exhaust conduit outside the EGR cooler. In this way, a portion of the exhaust passages mounted outside the EGR cooler in common engine systems prior to the junction may be integrated within the proposed EGR cooler with two separate exhaust passages. For example, by merging the exhaust gases to form a single exhaust conduit outside and downstream the EGR cooler, it is possible to create a more compact EGR system that may be mounted to the engine.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.